The calreticulin gene has nine exons and most of the frequent mutations screened and observed in the 9 th exon in myeloproliferative neoplasm patients, especially essential thrombocythemia and primary myelofibrosis. In the current study, an uncommon calreticulin mutation was observed in a 51 y old man with a polycythemia vera phenotype. Somatic novel homozygous mutations affect exon 9 of the calreticulin gene. These recent genetic variations were not reported in previous studies. Molecular screening of calreticulin may be important for polycythemia vera patients that are negative for the Janus kinase 2 V617F and exon 12 Janus kinase 2. A total of 11 negative Janus kinase 2 V617F polycythemia vera patients were previously diagnosed by the amplification refractory mutation system-polymerase chain reaction technique. Sanger sequencing was performed to screen exon 12 of the Janus kinase 2 gene and the last exon of the calreticulin gene. In addition, all 11 negative V617F patients were wild for exon 12 of the Janus kinase 2 gene. The calreticulin lesion in myeloproliferative neoplasms as a second biomarker, particularly in essential thromobocythemia and primary myelofibrosis, is more informative for diagnosis. Molecularly, in negative Janus kinase 2 V617F and exon 12 patients with polycythemia vera phenotypes, genotyping calreticulin may be useful.